It's my understanding that in Canada people who are trained to kill (soldiers, martial arts black belts, etc) come under higher scrutiny in such situations for just that fact...they should be able to asses just how much force is needed better than the average person and be able to control themselves better than the average person.

My old Kung Fu instructor used to tell me that the sign of a good martial artist boiled down to 2 things. The first was intent...without intent you'll never succeed. The second was the ability to control that intent as if it's unrestrained it won't be effective.

He was very good at training a balance of the 'assume the other person is going to kill you at all times' mentality combined with the ability to only use what's needed to get the job done without going overboard.